Blood pressure measuring mechanism

ABSTRACT

An apparatus for observing and measuring the complete range of arterial blood pressures. A small casing is provided having a cavity. The cavity is sealed at one end by a flexible membrane and at the other by a pressure responsive transducer. The casing has a ridge portion for positioning over an arterial duct complimentary to the duct. As pressure changes in the duct, the voltage output of the transducer varies representative of the duct pressure.

I United States Patent 1 1 3,704,708

Iberall 1 Dec. 5,1972

54] BLOOD PRESSURE MEASURING 3,400,709 9/1968 Funfstuck ..12s/2.0s DMECHANISM 3,535,067 10/1970 Lesher et al ..12s/2.0s P

3,456,648 7/1969 Lee et a1 ..l28/2.05 O [72] Inventor Arthur menu Radnor618,049 1/1899 Barnard et al. ..12s/2.0s N [73] Assignee: GeneralTechnical Services, Inc. 3,040,737 6/1962 Kompelien et al ..128/2.05 E

[22] i y 4, 1970 FOREIGN PATENTS OR APPLICATIONS 1 1 PP N 34,341 846,8868/1952 Germany ..12s/2.0s N

Related Application Data Primary Examiner-William E. Kamm [63]Continuation-impart of Ser. No. 658,487, Aug. 4, AttorneyMo1inare,Allegretti, Newitt & Witcoff 1967, abandoned.

[57] ABSTRACT v An apparatus for observing and measuring the [58] FieldofSearch..128/2631536313365 AG 205 cmplete 5; medal A 3 casing is provie aving a cavity. e cavity is se e 128/205 205 205 205 205 V at one endby a flexible membrane and at the other by 56] References Cited apressure responsive transducer. The casing has a ridge portion forpositioning over an arterial duct UNITED STATES PATENTS complimentary tothe duct. As pressure changes in the duct, the voltage output of thetransducer varies 3,230,950 1/1966 Buffington ..128/2.05 Rrepresentative of the duct pressure 3,102,534 9/1963 Bigliano et a]..l28/2.05 N

2 Claims, 9 Drawing Figures PATENT EUDEII 5 I972 TRANSDUCER SHEEI10F2INVENTOR. 2 ART/Ill? S IBERALL 5/A Mo Mm #119 072 N 5 /fu/ Q.

ATTORNEYS BLOOD PRESSURE MEASURING MECHANISM CROSS REFERENCE TO RELATEDAPPLICATION This is a continuation-in-part of my copending parentapplication entitled BLOOD PRESSURE MEA- SURING MECHANISM, by Arthur S.Iberall, Ser. No. 658,487, tiled Aug. 4, 1967. The parent applicationwas abandoned on May 6, 1970.

BACKGROUND OF THE INVENTION This invention relates to blood pressuremeasuring devices and, more particularly, to a simple, easily operabledevice for measuring the entire range of pressures in a vascular system.

The measurement of the pressure that blood exerts on the walls of thearteries provides one means for physicians to determine whether apatient is healthy. The blood pressure varies with each heart beat, and,in fact, varies between a high and low level, more commonly known as thesystolic and diastolic pressures. These pressures are obtained by usinga stethoscope and a sphygmomanometer.

The sphygmomanometer measures the blood pressure by comparing thepressure in the main artery of the arm with the pressure in aninflatable cuff wrapped around the arm. The inflated cuff stops the flowof blood through the artery. A valve allows the air pressure in the cuffto be reduced to the point where blood again may flow through theartery. When blood does begin to flow again through the artery thephysician will hear through his stethoscope a loud booming noise whichis coincident with the pulse beats of the heart. Upon first hearingthese pulse beats, the physician will be aware that blood is spurtingthrough the artery and that the pressure in the cuff, as indicated in amercuryfilled pressure gauge, is just below the high blood pressure ofthe patient.

As the physician continues to lower the cuff pressure he will no longerhear a noise in the stethoscope. Blood will then be flowing freelythrough the artery and the pressure at which this happens is likewisenoted on the mercury pressure gauge and recorded as the low bloodpressure of the patient. An average blood pressure is 120/70 which means120 millimeters of mercury pressure, is the maximum blood pressure and70 millimeters of mercury is the minimum blood pressure. Thiscorresponds to 2.3 and 1.3 pounds of pressure per square inchrespectively.

The sphygmomanometer is utilized basically to measure only the maximumand minimum blood pressures in an artery. Also, it must be used incombination with a stethoscope. More useful information could beobtained if there were some easy means to observe the behavior of theblood pressure between the maximum and the minimum. Such data would beanalogous to the electric impulse data garnered by an electrocardiogram.In addition to providing information about the heart beat itself, such adevice would give some indication of the state of health of the arterialvascular system.

A known prior art device, for example the device shown in French Pat.No. 1,285,774 employ a transducer in a casing for monitoring bloodpressure in a vascular duct. However, the device is not adapted to fitover and compliment the vascular duct so as to avoid cutting off offluid flow through the duct. Also the device provides no circuitry forreading out and separating AC and DC components of voltage from thetransducer.

Accordingly it is desirable to provide an improved blood pressuremeasuring mechanism adapted to fit over and compliment the vascularduct. It is also desirable to provide such a device capable of making ahighly accurate measurement of blood pressure. It is further desirableto provide such a device for monitoring which includes switchingcircuitry for selectively conducting (l) a product voltagerepresentative of the pressure of the device against the skin andpressure of fluid in the duct to be measured, or (2) a filtered voltagerepresentative of only the pressure of fluid in the duct.

SUMMARY OF THE INVENTION In a principal aspect, the present inventioncomprises a blood pressure measuring device which features, a housinghaving a lower ridge portion, a cavity defined in the housing, aflexible membrane sealing the cavity at one end, and a transducersecured in the housing adjacent the membrane. The lower ridge portiondefines a rectangular channel having two shoulders, one on each side ofthe channel. The membrane is fitted against the skin of a patient, therectangular channel fitting over and complimenting the vascular duct forwhich a pressure curve is desired. The shoulders engage covering aroundthe duct pressing it inwardly from the shoulders toward the membrane.

It is thus an object of this invention to provide an improved device forcontinually and accurately measuring the changing pressure of fluids ina vascular system.

It is a further object of the present invention to provide a simplyconstructed, economical device for measuring vascular system pressures.

Still another object of the present invention is to provide a devicewhich permits visual and recordable measurements of the pressure in avascular system.

These and other objects, features and advantages of the presentinvention will be more fully set forth in the detailed description whichfollows.

BRIEF DESCRIPTION OF THE DRAWINGS There is shown in the attached drawinga presently preferred embodiment of the present invention wherein likenumerals refer to like elements and wherein:

FIG. 1 is a perspective view illustrating the improved blood pressuremeasuring device positioned over the temporal artery;

FIG. 2 is an enlarged perspective view of the improved blood pressuremeasuring device;

FIG. 3A is an enlarged perspective view of a flexible membrane adaptedfor use with the device of FIG. 2',

FIG. 3 is a cross-sectional view of the improved blood pressuremeasuring device positioned against the skin of a patient over anartery;

FIG. 4 is a circuit diagram of the switching circuitry and recorder forcontinuously displaying the pressure sensed by the device of FIG. 1;

FIG. 5 is a circuit diagram of a preferred embodiment of the transduceremployed by the device of FIG. 1;

FIG. 6 is a perspective view illustrating an alternative embodiment ofthe blood pressure measuring device positioned over the temporal artery;

FIG. 7 is an enlarged perspective view of the blood pressure measuringdevice of FIG. 6 with the capillary being capped; and

FIG. 8 is a cross-sectional view of the blood pressure measuring deviceof FIG. 6 positioned against the skin of a patient over an artery.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, a strap 10serves to position the improved blood pressure measuring devicegenerally shown at 12 against an artery in the temple of the patient.

FIG. 2 is an enlarged view of the device 12 illustrated in FIG. 1. Thedevice 12 is comprised of a base block or housing 14 which has a ridgeportion 16 defined in the housing 14. The ridge portion 16 includes arectangular channel 18 and shoulders 20 and 22 adapted to fit over avascular duct.

FIG. 3 shows a cross-sectional view of the device in operative positionover a vascular duct 24. The housing of substantially rectangular shapehas a cavity 26 which is sealed from the atmosphere at one end by aflexible membrane or diaphragm 28. The bottom portion of the housing 14is shaped to define the rectangular channel 18 which fits incomplimentary fashion over the vascular duct 24 along a short distanceof the duct. Thus, as illustrated in FIG. 3, the housing 14 has asubstantially rectangular shape. The membrane 28 is positioned betweenshoulders 20 and 22 and fits against the upper surface of-therectangular channel 18. When the device is pressed against the skin 30of the patient, the shoulders 20 and 22 engage the skin 30 aligning withthe duct 24. In this position, the duct 24, situated in the tissue area38, is trapped between the shoulders 20 and 22 and pressed inwardly fromthe shoulders 20 and 22.

When the device 12 is positioned over the vascular duct 24, the duct 24is entrapped in the rectangular channel 18 between the shoulders 20 and22 and beneath the flexible membrane 28. The blood pressure measuringdevice 12 should be placed over a portion of the duct 24 lying in agroove defined in the skeletal structure of the animal for optimalresponse. For example, the bony groove 32 having upper curved regions 34and 36 will serve to cooperate with the rectangular channel 18 forentrapping the duct 24 beneath the membrane 28.

In practice the block 14 is constructed of a transparent moldablematerial such as acrylic and has overall dimensions of approximately 1centimeter in length and l centimeter in width by one-half centimeter indepth.

The membrane 28, shown more clearly in FIG. 3A, is a disk shapeddiaphragm of sponge material commonly identified under the trademarkSILASTIC. It has been found that a disk one-sixteenth inch thick andone-half inch in diameter will function acceptably.

A neck or raised portion 39 in the form of an annular disk is integrallymolded to the membrane 28. The neck 39 is adapted to fit snugly into thecavity 26 for sealing the cavity 26 and more accurately sensing thepressure of the duct 24. As flow of blood through the duct 24 en- Iargesor constricts the duct 24, the membrane 28 is caused to moveresponsively.

PREFERRED EMBODIMENT OF THE TRANSDUCER A fluid activated transducer 42is secured in the cavity 26 positioned to reflect changes of pressure atthe neck 39.of the diaphragm 28. The transducer 42 is one of the typecommonly known in the art.

Referring to FIGS. 4 & 5, the transducer 42 may take the form of aWheatstone Bridge 43 having fixed resistors 44, 45, 46 and 47 andvariable resistor 48. The variable resistor may be positioned on theneck 39 of the membrane 28 so that movement of the neck 39 causesphysical distortion of the variable resistor 48. The distortion variesthe resistance of resistor 48 and serves to produce a voltage across theoutput terminals 50 of the bridge 43 representative of the distortion.

Means for monitoring this voltage representative of pressure may takethe form of an oscilloscope or a recorder. A recorder is preferable asit will give continuous readings and record these readings for futurereference.

Power is supplied to the transducer 42 from a DC voltage source 51. Thepower from the voltage source 51 may be controlled by a single pole,single throw manually operable switch 51A in series with the voltagesource 5. As shown in FIG. 4, the switch 51A is in the off position.Voltage source 51 and switch 51A are in series across the inputterminals 513 of the transducer 42, which are also the input terminalsof the Wheatstone Bridge 43.

OPERATIVE PRINCIPLES OF THIS SYSTEM The principle operation of thissystem does not depend upon the elastic properties of the vascularsystem, but only upon the equal transmission of a hydrostatic pressurein all directions, if the pressure producing source is suitablyconfined. Thus when a plate is pressed down on a pressurized ductpossessing either small or large elastic resilience so as to flatten theduct at least in part, then the force required to flatten that areadivided by the area is a measure of the internal pressure in the duct.

This differs from cuff techniques which attempt to put an entire volumeinto hydrostatic pressure, and thereby to measure one or moreidentifiable events when an internal duct is constructed by externalhydrostatic forces.

In the present case, an attempt is made to flatten an internal duct.However, there is interposed tissue, in which both the duct and tissueare elastic. A solid backing is the preferred internal arrangement bywhich such flattening can be achieved. This can be realized in a numberof regions in the body, where an artery passes over a bony prominence.The temporal artery in the temple is a prime example. Against such abacking, an approximately triangular region can be confined in which theconfinement pressure is sufficient to flatten the duct into a desirableconfiguration, namely nearly triangular. Under these circumstances, theelasticity of duct, tissue, membrane, and springiness of the manometricsystem or fluid, provides a linear measure of pressure in the duct. Thecalibration constants a and b in p=duct pressure Ap=manometric pressuredepend on the tissue characteristics, duct characteristics, and thedegree to which the confining force is applied. The confining block isdesigned to provide automatic stops against the underlying bone, so thatconfining force is not a critical parameter. Thus calibration can beachieved for a subject by checking against a sphygmomanometer.

In practice the device of the present invention must be used on avascular duct which is near the surface of the body, for example, thetemporal artery.

POSITIONING OF THE MEASURING DEVICE Positioning of the device 12 overthe vascular duct 24 is important for the accuracy of this device. Thestrap should be placed on the head of the wearer and the measuringdevice 12 brought into approximate contact over the temporal artery.

When the device 12 is in this position, the transducer 42 will produce avoltage product having both AC and DC components. The AC voltagecomponent is representative of the fluctuating blood pressure of theduct 24, and the DC voltage component is representative of the constantoff-set pressure of the device 12 against the head of the wearer.Generally, the DC component of voltage will exceed the AC component ofvoltage by a multiple of ten or more. For example, an acceptable DCcomponent of voltage would be in the range of 10-18 millivolts.

A voltage below this range indicates that the device is not sufficientlymechanically coupled to the duct 24 to provide accurate readings of theblood pressure of the duct 24. A DC component of voltage in excess ofthis range (for example a voltage in excess of millivolts) indicatesthat the pressure of the device 12 against the head of the wearer isexcessive. This excess pressure could produce a cutting off of the flowof blood through the duct 24 and cause a termination of the accurateresponse of the monitoring device. Also, excessive pressure might damagethe elements of the transducer 42.

A monitoring circuit 54 has been provided for separating and reading outthe AC and DC components of voltage produced by the transducer 42. Thismonitoring circuit 54 includes a double pole, double throw switch 56,having movable contacts 58 and fixed contacts 60. The fixed contacts 60are connected to the input 61 of the recorder 52. The movable contacts58 are movable into contact with shunt contacts 62 and alternately withcapacitive filtering contacts 64.

With the switch 56 connected to shunting contacts 62, the AC and DCcomponents of voltage from the output 65 of the transducer 42 areconducted to the recorder 52. When the switch 56 is placed in contactwith the capacitive filtering leads 64, the capacitors 66 act as afilter with respect to the DC component of voltage from transducer 42and as a closed circuit or conductive path with respect to the ACcomponent voltage from transducer 42.

As has been described, the DC component of voltage exceeds the ACcomponent by a multiple of 10 or more. Accordingly, in the shunt mode,the output to the recorder 52 is approximately equal to the DC componentof voltage. A range switch 66 is provided on the recorder 52 forswitching the recorder range by a factor of 10. Accordingly, with therange switch in position A, the recorder is provided with a 0 to 3millivolt range, and with the range switch in position B, recorder 52 isprovided with a scale reading from 0-30 millivolts.

While the device is being positioned over the duct 24, the switch 56should be in the DC mode in contact with shunting leads 62 and the rangeswitch 66 of the recorder 52 should be in position B so as to have afull scale reading of 30 millivolts. In the present embodiment, it hasbeen found that an acceptable off-set value of DC voltage is between l0and 18 millivolts with an outside maximum of 20 millivolts. The strap 10should be adjusted over the duct 24 in such a fashion as to provide areading in this range.

After this initial adjustment has been made, the switch 56 should beplaced into the AC mode with movable contact members 58 in contact withcapaci-' tive filtering leads 64. The range switch 66 of the recorder 52should be moved into position A providing the recorder 52 with a fullscale reading of 3 millivolts. Having thus adjusted the monitoringcircuitry 54, the device 12 should be adjusted until the maximum signalamplitude is read out on the recorder 52. Next the offset pressureshould be decreased or increased until the signal amplitude is at amaximum.

The device of the present invention has been used successfully on thehuman arterial vascular system; however, the principle is not limited tothis system. Such a device may be used to measure pressure in anyvascular or fluid bearing system which transports material inelastically deformable tubes.

ALTERNATIVE EMBODIMENT In FIG. 6 a strap serves to position the bloodpressure measuring device generally shown at 102 against an artery inthe temple of the patient.

FIG. 7 is an enlarged view of the alternative device 102. The device 102is comprised of a base block 104 which has a curved lower portion 106adapted to fit over a vascular duct and to bear against a bony backingstructure 108. Extending through the top of the block 104 is a capillarytube 110 which is transparent to permit visual observation. Indicia 112are scribed at uniform linear intervals along the capillary tube. Theindicia 112 are optional and may not be advantageous when the bloodpressure device is used in combination with a photocell measurementapparatus. A removable cap 124 is positioned on the top of the openended capillary 110.

FIG. 8 shows a cross-sectional view of the device in operative positionover a vascular duct 1 14. The block 104 has a fluid filled inner cavity116 which is sealed from the atmosphere by a flexible membrane ordiaphragm 118. The block 104 has a substantially rectangular shape. Thebottom portion of the block 104 is shaped to define a curved surfacewhich will cover the vascular duct 114 along a short distance of theduct. Thus, as illustrated in FIG. 8, the curved surface is defined bythe membrane 1 l8 and the lower side portions 120 and 122 of the block104. The end portions of the block 104 are curved to fit over the duct114 as is illustrated by the lower curved end portion 106 in FIG. 7.

The capillary 110 extends through the block 104 from the cavity 116 andis temporarily sealed by the removable cap 124. Fluid 126 is situatedinside the cavity 1 16 and fills a portion of the interior of thecapillary 110. The device is pressed against the skin 128 of the patientand tends to pinch up the skin and trap the duct 114, which is situatedin the tissue area 130, against the bone 108.

The principal of operation does not depend upon the elastic propertiesof the vascular system, but only upon the equal transmission of ahydrostatic pressure in all directions, if the pressure producing sourceis suitably confined. Thus when a plate is pressed down on a pressurizedduct possessing either small or large elastic resilience so as toflatten the duct at least in part, then the force required to flattenthat area divided by the area is a measure of the internal pressure inthe duct.

in practice the device of the present invention must be used on avascular duct which is near the surface of the body, for example, thetemporal artery. Cap 124 is removed from the capillary 110 during theprocedure to locate the artery, since maximum deflections of the liquidlevel in the capillary 110 occur when the cap 124 is removed. Under thiscondition, the manometer is really being used as a displacement gauge ofthe elastic effect of pressure in the elastic duct which is elasticallydeforming the overlying tissue. In some crude way this deflection isalso proportional to pressure, but it depends on assuming elasticcharacteristics of all the tissue, and it depends critically onpositioning. This differs from confinement, with the manometer closed sothat a stiff manometric spring is presented to the tissue, sufficient todeform the arterial duct into triangular shape, but so shaped that theduct cannot be pinched off. Thus the artery is preferably confinedbetween the device 102 and a bony prominence such as illustrated by thebone 108 in FIG. 8.

After the artery is located, the cap 124 is placed on the capillary 110leaving a short air spring column 134 in the capillary. The fluid-gasfilled capillary now acts as a stiff spring relative to the arterialsegment with is covered by the device 102. Since the artery is confinedbetween the bone 108 and the device 102, the level of the liquid springis affected by the arterial expansion which distorts the membrane 118.Because the duct 114 and tissue 130 are confined, and the membrane 118,manometric fluid 126, and confined air spring column 134 are elastic,the displacement of the membrane 118 is directly and linearlyproportional to the pressure within the artery.

Experiments have been performed testing the device .wherein thevariation in the height of fluid in the capillary column was detected byan AC differential photocell apparatus 136. A continuous record of thepressure was obtained with a resolution sufficient to show the incisurain the pressure pulse.

While in the foregoing there has been set forth a preferred embodimentof the present invention, it is to be understood that all thoseembodiments obvious to persons skilled in the art and all thoseembodiments which are equivalent are to be included within the scope ofthe claimed invention.

What is claimed is:

1. A device for continuously monitoring internal pressure in a vascularsystem of a skeletal animal at a remote location comprising, incombination:

a housing having a lower ridge portion including a first shoulder on oneside thereof and a second shoulder on the other side thereof, saidshoulders defining a laterally extending, rectangular, openended channeltherebetween, said ridge portion adapted to fit over and complement avascular duct, said shoulders adapted to engage covering around thevascular duct and hold substantially at the sides of the vascular ductpressing the duct inwardly from the shoulders,

a flexible membrane secured to said housing at said rectangular channeland adapted to fit over said duct,

a transducer secured in said housing adjacent and coupledto saidmembrane for generating a voltage in response to pressure against saidmembrane,

means for passing only the AC component of voltage from said transducerconnected to the output of said transducer,

means for displaying a voltage, and

switching means connected to said display means for selectivelyconducting the output voltage from said transducer where only the ACcomponent of said voltage to said monitoring means such that the voltageof said transducer representative of the pressure of said device againstsaid animal and the pressure of said duct may be displayed on saiddisplay means, and alternatively, the AC component of said voltage,representative only of the pressure of said duct may be displayed onsaid display means.

2. The device of claim 1 wherein said flexible membrane is a spongeSILASTIC disc.

1. A device for continuously monitoring internal pressure in a vascularsystem of a skeletal animal at a remote location comprising, incombination: a housing having a lower ridge portion including a firstshoulder on one side thereof and a second shoulder on the other sidethereof, said shoulders defining a laterally extending, rectangular,open-ended channel therebetWeen, said ridge portion adapted to fit overand complement a vascular duct, said shoulders adapted to engagecovering around the vascular duct and hold substantially at the sides ofthe vascular duct pressing the duct inwardly from the shoulders, aflexible membrane secured to said housing at said rectangular channeland adapted to fit over said duct, a transducer secured in said housingadjacent and coupled to said membrane for generating a voltage inresponse to pressure against said membrane, means for passing only theAC component of voltage from said transducer connected to the output ofsaid transducer, means for displaying a voltage, and switching meansconnected to said display means for selectively conducting the outputvoltage from said transducer where only the AC component of said voltageto said monitoring means such that the voltage of said transducerrepresentative of the pressure of said device against said animal andthe pressure of said duct may be displayed on said display means, andalternatively, the AC component of said voltage, representative only ofthe pressure of said duct may be displayed on said display means.
 2. Thedevice of claim 1 wherein said flexible membrane is a sponge SILASTICdisc.